SIBO Guide 2026: Causes, Testing & Treatment Explained

Disclaimer: The information in this article is for educational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before making changes to your health regimen.

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Small intestinal bacterial overgrowth — SIBO — is one of the most under-diagnosed and over-treated conditions in functional medicine. Bacteria, normally abundant in the colon, colonise the small intestine in abnormally high numbers, fermenting carbohydrates before they can be absorbed and producing gases (hydrogen, methane, hydrogen sulphide) that cause bloating, pain, distension, and nutrient malabsorption. It is estimated to affect 6–15% of healthy adults and up to 80% of IBS patients.

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Key Terms Explained

Not familiar with a term? Our Gut Health & Microbiome Glossary explains every concept — with PubMed references.

Complete Guide

← Gut Health: The Complete Guide to Your Microbiome (2026)

This article is part of our comprehensive gut health series.

What Is SIBO and Why Does It Happen?

Under healthy conditions, the small intestine contains relatively few bacteria — typically 10³–10⁴ organisms per millilitre, compared to 10¹¹ per mL in the colon. Several mechanisms keep bacterial counts low: the migrating motor complex (MMC) — a wave of contractions that sweeps the small intestine every 90 minutes during fasting, clearing residual bacteria; stomach acid (pH 1.5–3.5, which kills most ingested pathogens); bile acids (bactericidal at small intestinal concentrations); and the ileocaecal valve (which prevents backflow from the colon). When any of these mechanisms fail, bacteria from the colon or oropharynx colonise the small intestine.

Common SIBO triggers: proton pump inhibitors (raise gastric pH, eliminating the acid barrier); motility disorders (including hypothyroidism, diabetes-related gastroparesis, and post-surgical adhesions that impair MMC function); structural abnormalities (diverticula, surgical blind loops); immune deficiency (IgA deficiency is particularly associated); and prior gastroenteritis triggering post-infectious IBS/SIBO.

^[3] 550mg × 3/day for 14 days Methane SIBO / IMO (Intestinal Methanogen Overgrowth) CH₄ gas; Methanobrevibacter smithii (archaea) Constipation-predominant, slow transit, fullness Rifaximin + Neomycin or Rifaximin + Metronidazole Hydrogen Sulphide SIBO (newly recognised subtype) H₂S gas; Desulfovibrio, Fusobacterium Diarrhoea, sulphur odour, abdominal pain Bismuth + Rifaximin; low-sulphur diet 🔬 Lactulose Breath Test Interpretation Positive H₂ SIBO: H₂ rise ≥ 20 ppm above baseline within 90 min after lactulose dose Positive CH₄ (IMO): CH₄ ≥ 10 ppm at any point during the test (even with flat H₂ curve) Gold standard: jejunal aspirate culture >10⁵ CFU/mL but impractical outside research settings 🌿 Herbal Antimicrobial Protocols Oil of oregano (carvacrol): broad-spectrum antimicrobial Berberine: reduces pathobiont growth Allicin (garlic-derived): effective vs methane SIBO Neem: biofilm disruption Protocol: 4-week course; equivalent to rifaximin in one RCT (Chedid et al., Global Adv Health Med 2014) Sources: Pimentel et al. Am J Gastroenterol 2020 · Ghoshal et al. JGH 2017 · Chedid et al. Glob Adv Health Med 2014

Fig. 1 — SIBO subtypes, breath test interpretation, and first-line treatment options including herbal protocols.

Diagnosing SIBO: The Breath Test

The lactulose hydrogen/methane breath test is the most widely available clinical tool. The patient ingests lactulose (a non-absorbable sugar) and exhales breath samples every 15–20 minutes for 3 hours. Bacteria in the small intestine ferment the lactulose and produce hydrogen or methane gas detectable in exhaled breath before colonic bacteria would have had time to ferment it. A hydrogen rise of ≥20 ppm above baseline within 90 minutes is considered positive for hydrogen SIBO; methane of ≥10 ppm at any point indicates intestinal methanogen overgrowth (IMO). Glucose breath testing is more specific but less sensitive — it only detects proximal SIBO.

Conventional Treatment: Rifaximin and Neomycin

Rifaximin (Xifaxan) is a non-absorbable antibiotic with activity concentrated in the GI tract. For hydrogen SIBO, rifaximin 550mg three times daily for 14 days achieves eradication in approximately 70% of cases. For methane SIBO (IMO), rifaximin is typically combined with neomycin 500mg twice daily (which targets archaea more effectively) — achieving ~85% eradication. Recurrence is the major clinical challenge; without addressing the underlying cause (motility, PPI use, ileocaecal valve dysfunction), SIBO returns within months in most patients.

How SIBO contributes to intestinal permeability, and the repair protocol for restoring the gut lining after treatment.

Diet Strategies: Low-FODMAP, Elemental & SCD

The low-FODMAP diet reduces fermentable substrates available to small intestinal bacteria, providing symptom relief without eradicating SIBO — typically used alongside antibiotic or herbal treatment. The elemental diet (pre-digested amino acids, glucose, and fats) starves bacteria entirely while maintaining nutrition; a 14-day elemental diet achieves SIBO eradication rates comparable to antibiotics (~80%) but requires significant compliance. The Specific Carbohydrate Diet (SCD) eliminates disaccharides and most polysaccharides, reducing fermentation substrate.

Why digestive enzyme support is important after SIBO eradication, and how to choose the right formula for your symptoms.

For the complete context on how SIBO fits into gut health restoration, read our complete gut health guide.

References & Scientific Sources

[1] Ghoshal UC, Shukla R, Ghoshal U (2017). Small Intestinal Bacterial Overgrowth and Irritable Bowel Syndrome: A Bridge between Functional Organic Dichotomy. Gut Liver 11(2):196–208. https://pubmed.ncbi.nlm.nih.gov/28274108/
[2] Pimentel M et al. (2020). ACG Clinical Guideline: Small Intestinal Bacterial Overgrowth. Am J Gastroenterol 115(2):165–178. https://pubmed.ncbi.nlm.nih.gov/32023228/
[3] Pimentel M et al. (2011). Rifaximin therapy for patients with irritable bowel syndrome without constipation. N Engl J Med 364(1):22–32. https://pubmed.ncbi.nlm.nih.gov/21208106/
[4] Chedid V et al. (2014). Herbal therapy is equivalent to rifaximin for the treatment of small intestinal bacterial overgrowth. Glob Adv Health Med 3(3):16–24. https://pubmed.ncbi.nlm.nih.gov/24891990/
[5] Lauritano EC et al. (2008). Small intestinal bacterial overgrowth recurrence after antibiotic therapy. Am J Gastroenterol 103(8):2031–2035. https://pubmed.ncbi.nlm.nih.gov/18802998/
[6] Shah A et al. (2018). Small Intestinal Bacterial Overgrowth in Irritable Bowel Syndrome: A Systematic Review and Meta-Analysis of Case-Control Studies. Am J Gastroenterol 115(2):190–201. https://pubmed.ncbi.nlm.nih.gov/31117145/

Frequently Asked Questions

What are the symptoms of SIBO?+

Common symptoms: bloating (progressive throughout the day), abdominal distension, excess gas, abdominal pain, diarrhoea (hydrogen SIBO) or constipation (methane SIBO), nutrient deficiencies (iron, B12, fat-soluble vitamins), and weight loss in severe cases.

How is SIBO diagnosed?+

The lactulose or glucose hydrogen/methane breath test is the most common tool. Positive: H₂ rise ≥20 ppm within 90 min, or CH₄ ≥10 ppm at any point. Gold standard is jejunal aspirate culture (>10⁵ CFU/mL) but requires endoscopy.

Can SIBO be treated without antibiotics?+

Yes. A 2014 RCT found herbal antimicrobials (oil of oregano, berberine, allicin, neem) achieved eradication rates equivalent to rifaximin. A 14-day elemental diet achieves ~80% eradication comparable to antibiotics.

Why does SIBO keep coming back?+

Recurrence occurs when the underlying cause isn't addressed — most commonly impaired migrating motor complex (MMC) function, PPI use (reduces gastric acid barrier), ileocaecal valve dysfunction, or rapidly re-colonising dietary habits.

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